Serum Iron Levels are Linked to the Metabolic Syndrome

Summarized by Robert W. Griffith, MD
December 10, 2004

Introduction

People who have hemochromatosis - an inherited disease in which there's an overload of iron in the body - often develop type 2 diabetes. And a study found that, indeed, increased heme-iron intake from red meat was clearly associated with an increased risk of diabetes (see the first link below). Although that study couldn't directly relate overall iron in the diet with a risk of diabetes, the suspicion was there. Now a study has examined if increased levels of iron in the blood are linked to the occurrence of the metabolic syndrome, one common feature of which is a raised fasting blood sugar level (i.e. pre-diabetes). The investigators from Johns Hopkins University have published their findings in Diabetes Care, and we summarize their report here.

What was done

The scientists used data from the Third National Health and Nutrition Examination Survey (NHANES III) gathered between 1988 and 1994. This involved a nation-wide survey sample with a home interview and a detailed clinical examination. They limited their analysis of results from healthy NHANES III participants aged 20 or older who weren't pregnant or nursing.

The metabolic syndrome was defined as the presence of at least 3 of the following:

Abdominal obesity - waist circumference greater than 102 cm (40 inches) in men, or 88 cm (35 inches) in women
Blood triglyceride level 150 mg/dL or above (1.7 mmol/L or above)
HDL-cholesterol 40 mg/dL (1.04 mmol/L) or below in men, or 50 mg/dL (1.29 mmol/L) or below in women.
High blood pressure - 130/85 mm Hg or higher, or taking blood pressure medication
High fasting glucose level - 110 mg/dL (6.1 mmol/L) or above

(If you want to see if you may have the metabolic syndrome, go to the second link below.)

Serum ferritin levels¹ were measured in all participants. Ferritin quartiles - equal-sized groups of participants based on their ferritin levels (low, low-mid, high-mid, and high) - were formed for three separate classes of subjects: premenopausal women, post-menopausal women, and men. (Women who are menstruating have lower iron stores, naturally.)

Tests were also done to search for possible insulin resistance and the presence of undiagnosed hemochromatosis.

What was found

First, the investigators excluded people with likely hemochromatosis from further analyses. This left 6,000 subjects in the final sample. The average ferritin levels in pre-menopausal women, post-menopausal women, and men were: 33.6, 93.4, and 139.9 microgram/liter, respectively.

The metabolic syndrome was more common in the high ferritin quartile compared with the low ferritin quartile, for men and both classes of women. For instance, the rates of metabolic syndrome in men with the highest and lowest ferritin levels were 27% and14%, respectively. In premenopausal women these rates were 15% and 6%, respectively.

Individual components of the metabolic syndrome also correlated with the serum ferritin levels - especially raised triglyceride and raised fasting glucose levels.

Insulin resistance was also increased, corresponding to the ferritin quartiles low, low-mid, high-mid, and high. Adjusting for age, smoking, alcohol intake, and BMI made no difference to these findings.

What this means

Body iron stores are clearly linked with the occurrence of the metabolic syndrome and, as the earlier study cited, with the development of type 2 diabetes. It's likely that the chief effect of raised iron levels is connected with impaired insulin resistance, with the other findings following on from this. But is this connection one of cause-and-effect, or are ferritin levels just a 'marker' of insulin resistance?

This question is obviously one that needs answering if the cause of type 2 diabetes is to be unraveled. More research is necessary, as we always seem to say. However, there is a take-home message: try not to let your iron levels get too high by eating less red meat (which seems to be a relevant source of heme-iron), and try to eat more veggies, for hundreds of good reasons. Of course, don't lose sight of the fact that some elderly people just don't get enough iron in their diet. If you aren't sure, ask your doctor about a serum iron test.

Source

Serum ferritin and risk of the metabolic syndrome in U.S. adults. M. Jehn, JM. Clark, E. Guallar, Diabetes Care, 2004, vol. 27, pp. 2422--2428

Footnotes
1. Ferritin is a protein that stores iron in the body. The serum ferritin level -- the amount of ferritin in your blood -- is directly proportional to the amount of iron stored in your body.